There seems to be more - a lot more - so why am I worried? 9.3.0 had a number of bugs that 9.3.1 was supposed to fix. Even if 9.3.1 fixed all the known issues, isn't it likely that all these new features have introduced bugs of their own?

Well, let's take a look at one of the ReadMe's: Hyperion Reporting & Analysis (basically, all of BI+ except Essbase, all of Shared Services, User Provisioning, etc.). This document is 60 pages long. Pages 43-58 highlight the defects fixed in 9.3.1. Pages 10-43 detail the known issues still in 9.3.1 when they issued it. Now to be fair, the defects fixed are usually listed on one or two lines while the known defects often take up a paragraph or more, but 33 pages of known defects in just BI+ and the supporting layers?